Surveys by the polling firms Datafolha and IBOPE found Neves with backing from 51 percent of voters polled this week, while the president was supported by 49 percent. Both polls had a margin of error of two percentage points.

Rousseff of the leftist Workers Party won 42 percent of the votes cast Sunday in the first-round election. Neves of the centrist Party of Social Democracy finished second with 34 percent to earn a spot in the runoff.

Former environment minister Marina Silva was third with 21 percent, but she has not said whether she will support either of the candidates in the runoff.